Transmitting apparatus, receiving apparatus, transmission method, and reception method

ABSTRACT

A transmission frame generating device includes a control information signal generator and a frame former. The control information signal generator generates a modulation method information signal indicating a modulation method of a data signal and an error correction method information signal indicating an error correction method of the data signal. The frame former forms the transmission frame by repeating and discretely arranging the same modulation method information signal on a first multiple of a plurality of subcarriers on a frequency axis and by repeating and discretely arranging the same error correction method information signal on a second multiple of the plurality of the subcarriers on the frequency axis.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/957,748, filed Aug. 2, 2013, which is a continuation of U.S.patent application Ser. No. 11/940,381, filed Nov. 15, 2007, which is acontinuation of U.S. patent application Ser. No. 11/413,155, filed Apr.28, 2006, now U.S. Pat. No. 7,328,389 which is a continuation of U.S.patent application Ser. No. 10/466,103, filed Jul. 18, 2003, now U.S.Pat. No. 7,069,489, which is the U.S. National Stage of InternationalApplication No. PCT/JP02/11921, filed Nov. 15, 2002, which claims thebenefit of Japanese Application No. 2001-356400, filed Nov. 21, 2001,the disclosures of which are expressly incorporated herein by referencein their entireties.

The present invention relates to a transmitting apparatus, receivingapparatus, transmission method, and reception method, and is suitablefor application to a digital radio communication system in which themodulation method or error correction method is changed adaptivelyaccording to the propagation path environment, for example.

BACKGROUND ART

Conventionally, various kinds of system control are carried out in aradio communication system in order to perform communication with highquality and high efficiency. An example is a radio communication systemin which the modulation method or error correction method is switchedadaptively according to the state of the propagation path. In this kindof system, the current propagation path state is determined based on theSIR (Signal to Interference Ratio) of a signal that atransmitting/receiving apparatus receives from a communicating party, orthe like.

In practice, when the propagation path state is good, information dataundergoes digital modulation using an M-ary modulation method with alarge information bearing capacity per symbol, such as 64QAM, forexample, and is transmitted with the addition of an error correctioncode with a high degree of redundancy as an error correction method.When the propagation path state is poor, on the other hand, informationdata undergoes digital modulation using a modulation method with a smallinformation bearing capacity per symbol, such as 16QAM or QPSK, forexample, and is transmitted with the addition of an error correctioncode with a low degree of redundancy as an error correction method.

Thus, in this kind of radio communication system, it is necessary tocommunicate to the receiving side the modulation method used to modulatea transmit signal and the error correction method used for errorcorrection processing. A receiving apparatus has a plurality ofdemodulation sections corresponding to a plurality of modulationmethods, and a plurality of error correction decoding sectionscorresponding to a plurality of error correction methods, and restoresthe original data by executing demodulation processing and errorcorrection processing in accordance with a communicated modulationmethod information signal and error correction information signal.

An example of a known frame configuration for arranging signalsindicating a modulation method within a transmit frame is that describedin “Development of an Adaptive Modulation System for Land MobileCommunications—Outline of the Scheme—”, Hamaguchi et al., IEICECommunications Society Conference B-5-135 pp. 388, September 1997.

FIG. 1 shows this frame configuration. Located in order from the startof the frame are one ramp symbol R, six synchronization symbols SW, onepilot symbol P, one modulation method information symbol I, and 18 datasymbols DATA.

A receiving apparatus that receives a signal with this kind of frameconfiguration determines the modulation method of data symbols DATA frommodulation method information symbol I, and demodulates data symbolsDATA using a demodulation method corresponding to the determinedmodulation method.

If, in the receiving apparatus, determination of modulation methodinformation symbol I or an error correction method information symbol(not shown) is incorrect, the data obtained by demodulation and decodingof data symbols DATA will be incorrect. It is therefore important formodulation method information and error correction method information tobe transmitted to the receiving apparatus correctly.

However, in radio communications, there is a risk of modulation methodinformation and error correction method information being erroneouslydetermined on the receiving side due to noise, or fading caused bypropagation path fluctuations, resulting in a reduction in communicationquality.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a transmittingapparatus, receiving apparatus, transmission method, and receptionmethod that make it possible for the modulation method and errorcorrection method of a digitally modulated signal to be determinedcorrectly on the receiving side, enabling communication quality to beimproved.

This object is achieved by, in a communication system in whichpropagation path error tolerance is improved by switching the modulationmethod or error correction method adaptively according to the state ofthe propagation path, transmitting signals indicating the modulationmethod and error correction method used by the transmitting sidearranged at discrete locations within the same frame.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing a conventional transmit frame configuration;

FIG. 2 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 1 of the present invention;

FIG. 3 is a drawing showing a transmit frame configuration according toEmbodiment 1;

FIG. 4 is an I-Q plane diagram provided to explain a case wheremodulation method information is QPSK modulated;

FIG. 5 is an I-Q plane diagram provided to explain a case where errorcorrection method information is BPSK modulated;

FIG. 6 is a block diagram showing the configuration of a receivingapparatus according to Embodiment 1 of the present invention;

FIG. 7 is a block diagram showing the configuration of a modulationmethod and error correction method estimation section;

FIG. 8 is a drawing showing the received field strength of a receivedsignal when fading or propagation path fluctuations are experienced;

FIG. 9 is a block diagram showing the configuration of a transmittingapparatus according to Embodiment 2;

FIG. 10(A) is a drawing showing a case where modulation methodinformation symbols and error correction method information symbols arearranged discretely in the frequency direction in an OFDM signal;

FIG. 10(B) is a drawing showing a case where modulation methodinformation symbols and error correction method information symbols arearranged discretely in the time direction in an OFDM signal; and

FIG. 11 is a block diagram showing the configuration of a receivingapparatus according to Embodiment 2.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanying drawings, embodiments of thepresent invention will be explained in detail below.

Embodiment 1

FIG. 2 shows the configuration of a transmitting apparatus according toEmbodiment 1 of the present invention. Transmitting apparatus 100 canselect an error correction method and modulation method adaptivelyaccording to the state of the propagation path. In transmittingapparatus 100, a transmit digital signal Dl is input to an errorcorrection A encoder 101 and error correction B encoder 102.

Error correction A encoder 101 and error correction B encoder 102perform error correction processing with different degrees ofredundancy. Specifically, error correction B encoder 102 performs errorcorrection processing with a higher degree of redundancy than errorcorrection A encoder 101, as a result of which error correction Bencoder 102 obtains error correction coded data with higher errortolerance. Error correction coded data obtained by error correction Aencoder 101 and error correction B encoder 102 is sent to a digitalsignal selection section 103.

Transmitting apparatus 100 has a modulation method and error correctionmethod decision section 104, to which a propagation path estimationsignal S1 is input. This propagation path estimation signal S1 isobtained based on the SIR (Signal to Interference Ratio), etc., of asignal received from a communicating radio station by the receivingsection of transmitting apparatus 100 (not shown).

Modulation method and error correction method decision section 104decides the modulation method and error correction method in accordancewith propagation path estimation signal S1. In actuality, when theeffects of fading fluctuations or noise are great, and a propagationpath estimation signal S1 indicating that the propagation path state ispoor is input, a modulation method with good error tolerance such asBPSK (Binary Phase Shift Keying) or QPSK, for example, is selected asthe modulation method, and an error correction method with a high degreeof redundancy is decided on as the error correction method.

Modulation method information S2 and error correction method informationS3 decided by modulation method and error correction method decisionsection 104 are sent to digital signal selection section 103, atransmission baseband signal selection section 106, and a controlinformation modulation section 105.

Digital signal selection section 103 selects the output of either errorcorrection A encoder 101 or error correction B encoder 102 based onerror correction method information S3, and sends this output to a BPSKmodulation section 107, QPSK modulation section 108, 16QAM modulationsection 109, and 64QAM modulation section 110.

Modulation sections 107 through 110 execute digital modulationprocessing on the digital signal input from digital signal selectionsection 103, and send signals that have undergone modulation processingto transmission baseband signal selection section 106. Transmissionbaseband signal selection section 106 selects a modulated signal fromamong the input plurality of modulated signals in accordance withmodulation method information S2. For example, when the propagation pathstate is poor and modulation method information S2 indicating BPSKmodulation or QPSK modulation is input, a BPSK modulated signal or QPSKmodulated signal is output selectively in accordance with this input.

The modulated signal selected by transmission baseband signal selectionsection 106, and signals indicating the modulation method and errorcorrection method modulated by control information modulation section105, are input to a frame configuration section 111. Control informationmodulation section 105 executes modulation processing with high errortolerance, such as BPSK modulation or QPSK modulation, on input signals.By this means, the error tolerance of signals relating to the modulationmethod and error correction method, which is extremely importantinformation, is raised on the receiving side.

Frame configuration section 111 according to this embodiment configuresa transmit frame as shown in FIG. 3, comprising, in order from the startof the frame, one pilot symbol P, three consecutive modulation methodinformation symbols MX, three consecutive error correction methodinformation symbols CX, 128 data symbols DATA, a pilot symbol P, datasymbols DATA, a pilot symbol P, a 10-symbol unique word UW, a pilotsymbol P, modulation method information symbols MY, error correctionmethod information symbols CY, data symbols DATA, a pilot symbol P, datasymbols DATA, and a pilot symbol P.

Here, modulation method information symbols MX and modulation methodinformation symbols MY are the same symbols, and error correction methodinformation symbols CX and error correction method information symbolsCY are the same symbols. Thus, frame configuration section 111 placesmodulation method information symbols MX and MY, and error correctionmethod information symbols CX and CY, discretely within the same frame.In other words, modulation method information symbols MX and modulationmethod information symbols MY are placed at different locations in theframe, and error correction method information symbols CX and errorcorrection method information symbols CY are placed at differentlocations in the frame.

The way in which modulation of a consecutive plurality of symbols (inthe case of this embodiment, three symbols) indicating modulation methodinformation is carried out by control information modulation section 105will now be described. To consider the case where the three consecutivemodulation method information symbols MX and MY are created by QPSKmodulation as shown in FIG. 4, there is a method whereby, for example,signal point 201 is mapped at modulation method information symbols MXand MY when the information symbol modulation method is BPSK modulation,signal point 202 is mapped in the case of QPSK modulation, signal point203 is mapped in the case of 16QAM, and signal point 204 is mapped inthe case of 64QAM.

As another way of performing modulation, there is a method whereby, forexample, mapping is performed at 201, 202, and 203 in temporal orderwhen the information symbol modulation method is BPSK modulation, at202, 204, and 203 in temporal order in the case of QPSK modulation, at204, 201, and 203 in temporal order in the case of 16QAM, and at 202,204, and 201 in temporal order in the case of 64QAM.

The way in which modulation of a consecutive plurality of symbols (inthe case of this embodiment, three symbols) indicating error correctionmethod information is carried out will now be described. To consider thecase where the three consecutive error correction method informationsymbols CX and CY are created by BPSK modulation as shown in FIG. 5,there is a method whereby, for example, signal point 301 is mapped aterror correction method information symbols CX and CY when errorcorrection method A is used, and signal point 302 is mapped when errorcorrection method B is used.

As another way of performing modulation, there is a method whereby, forexample, mapping is performed at 301, 302, and 302 in temporal orderwhen error correction method A is used, and at 302, 301, and 301 intemporal order when error correction method B is used.

When the former method is used here (when mapping is performed withsignal points fixed), high-precision estimation is possible with fewsymbols, and therefore the modulation method and error correction methodcan be estimated on the receiving side by the simple method of BPSK orQPSK modulation method detection. When the latter method is used (whensignal points are mapped in temporal order), on the other hand, even ifthere are no symbols for time synchronization of the transmittingapparatus and receiving apparatus, modulation method information symbolsand error correction method information symbols can be used as symbolsfor time synchronization of the transmitting apparatus and receivingapparatus. On the other hand, complex computations known as serialcorrelation computations are necessary in the receiving apparatus.

The signal output from frame configuration section 111 undergoesdigital-analog conversion and signal amplification processing by a radiosection 112, and is then transmitted by an antenna 113.

FIG. 6 shows the configuration of a receiving apparatus 500 thatreceives and demodulates a signal transmitted from transmittingapparatus 100. Receiving apparatus 500 executes predetermined radioreception processing such as amplification processing and analog-digitalconversion processing in a radio section 502 on a reception signalreceived by an antenna 501, thereby obtaining an orthogonal basebandsignal, and sends this signal to detection sections 503 through 506 anda modulation method and error correction method estimation section 507.

Detection sections 503 through 506 comprise a BPSK detection section503, QPSK detection section 504, 16QAM detection section 505, and 64QAMdetection section 506. The received baseband signals detected bydetection sections 503 through 506 are sent to a received digital signalselection section 508.

Modulation method and error correction method estimation section 507detects modulation method information symbols MX and MY, and errorcorrect ion method information symbols CX and CY, shown in FIG. 3, fromthe received orthogonal baseband signal, estimates the modulation methodand error correction method based on these information symbols MX, MY,CX, and CY, and sends estimation result S10 to received digital signalselection section 508 and a signal selection section 509.

Modulation method and error correction method estimation section 507 isconfigured as shown in FIG. 7. That is to say, in modulation method anderror correction method estimation section 507, the received orthogonalbaseband signal output from radio section 502 is input to a modulationmethod and error correction method signal detection section 520.Modulation method and error correction method signal detection section520 performs coherent detection of modulation method information symbolsMX and MY and error correction method information symbols CX and CYbased on unique word UW contained in the received orthogonal basebandsignal, and by executing BPSK demodulation processing or QPSKdemodulation processing thereon, detects and demodulates modulationmethod information symbols MX and MY and error correction methodinformation symbols CX and CY.

A modulation method and error correction method information Xdetermination section 521 determines and detects modulation methodinformation symbols MX and error correction method information symbolsCX shown in FIG. 3 from the detected modulation method informationsymbols MX and MY and error correction method information symbols CX andCY. Similarly, a modulation method and error correction methodinformation Y determination section 522 determines and detectsmodulation method information MY and error correction method informationCY shown in FIG. 3 from the detected modulation method informationsymbols MX and MY and error correction method information symbols CX andCY.

Here, as is clear from FIG. 3, these modulation method informationsymbols MX and error correction method information symbols CX, andmodulation method information symbols MY and error correction methodinformation symbols CY, are arranged discretely at separate locations ina transmission frame, and are arranged at regular intervals. Therefore,modulation method and error correction method information Xdetermination section 521 and modulation method and error correctionmethod information Y determination section 522 can easily determine anddetect these information symbols based on pilot symbols P, for example.

A modulation method and error correction method information X receptionpower calculation section 523 calculates the reception power ofmodulation method information symbols MX and error correction methodinformation symbols CX. Similarly, a modulation method and errorcorrection method information Y reception power calculation section 524calculates the reception power of modulation method information symbolsMY and error correction method information symbols CY. Actually, thelocations of modulation method information symbols MX and errorcorrection method information symbols CX, and modulation methodinformation symbols MY and error correction method information symbolsCY, arranged discretely within a frame, are detected based on pilotsymbols P and unique word UW, and the reception power of modulationmethod information symbols MX and error correction method informationsymbols CX, and the reception power of modulation method informationsymbols MY and error correction method information symbols CY, arecalculated.

A modulation method and error correction method decision section 525weights modulation method information MX and error correction methodinformation CX obtained by means of modulation method and errorcorrection method information X determination section 521 with thereception power obtained by means of modulation method and errorcorrection method information X reception power calculation section 523.Similarly, modulation method and error correction method decisionsection 525 weights modulation method information symbols MY and errorcorrection method information symbols CY obtained by means of modulationmethod and error correction method information Y determination section522 with the reception power obtained by means of modulation method anderror correction method information Y reception power calculationsection 524.

Then modulation method and error correction method decision section 525decides the modulation method and error correction method by addingreception power weighted modulation method information symbols MX and MYand error correction method information symbols CX and CY. Thus,modulation method and error correction method estimation section 507detects the reception power at discrete locations for modulation methodinformation symbols MX and MY and error correction method informationsymbols CX and CY arranged discretely within a transmission frame, andby weighting and adding modulation method information symbols MX and MYand error correction method information symbols CX and CY according tothis reception power, obtains final modulation method information anderror correction method information.

Returning now to FIG. 6, receiving apparatus 500 will be described.Received digital signal selection section 508 selects from the outputsof BPSK detection section 503, QPSK detection section 504, 16QAMdetection section 505, and 64QAM detection section 506, the outputcorresponding to the modulation method estimated by modulation methodand error correction method estimation section 507, and then sends thisoutput to an error correction A decoder 510 and error correction Bdecoder 511.

Reception demodulated signals decoded by error correction A decoder 510and error correction B decoder 511 using different error correctionmethods are sent to signal selection section 509. Signal selectionsection 509 selects from error correction A decoder 510 and errorcorrection B decoder 511 the output corresponding to the errorcorrection method estimated by modulation method and error correctionmethod estimation section 507, and outputs this as the final receptiondecoded signal.

In the above configuration, transmitting apparatus 100 adaptivelyperforms digital modulation of data symbols DATA using modulationmethods with different error tolerance, and error correction processingusing error correction methods with different error tolerance, accordingto the state of the propagation path.

In addition, transmitting apparatus 100 transmits with modulation methodinformation symbols MX and MY and error correction method informationsymbols CX and CY arranged discretely within a transmit frame.Modulation method information symbols MX and MY and error correctionmethod information symbols CX and CY are transmitted modulated using amodulation method with good error tolerance, such as BPSK modulation orQPSK modulation.

On receiving this transmit signal, receiving apparatus 500 firstcalculates the reception power of discretely arranged modulation methodinformation signals MX and MY and error correction method informationsignals CX and CY. As shown in FIG. 8, the reception power of a receivedsignal varies over time due to the effects of fading and so forth. As aresult, of discretely arranged modulation method information signals MXand MY and error correction method information signals CX and CY,modulation method information signal MX and error correction methodinformation signal CX may have low reception power (received fieldstrength), for example, while modulation method information signal MYand error correction method information signal CY have high receptionpower.

In general, a signal of higher reception power has a lower error rate indemodulation, and therefore receiving apparatus 500 multipliesmodulation method information signal MX and error correction methodinformation signal CX, whose reception power is low, by a low-valuedweighting coefficient, and multiplies modulation method informationsignal MY and error correction method information signal CY, whosereception power is high, by a high-valued weighting coefficient. Theseadded values are then taken as final modulation method information anderror correction method information.

As a result, correct modulation method information and error correctionmethod information can be obtained even in the event of propagation pathfluctuations or fading.

Receiving apparatus 500 selects data demodulated by means of ademodulation method corresponding to the acquired modulation methodinformation, and selects reception decoded data that has undergone errorcorrection decoding processing corresponding to the acquired errorcorrection method information, to obtain final receive data.

As a result, it is possible to obtain a signal that has been demodulatedand decoded by means of an appropriate modulation method and anappropriate error correction method, thereby enabling reception qualityto be improved.

A description will be given here of a discrete arrangement method forfurther improving the estimation precision for modulation method anderror correction method information. In order to restore modulationmethod and error correction method information correctly, the receivedfield strength of each information symbol need only be at or above acertain level. Thus, it is sufficient if there are symbols whosereceived field strength is at or above a certain level among discretelyarranged modulation method information and error correction methodinformation symbols.

Thus, in this embodiment, it is proposed that discretely arrangedtemporal locations be selected taking account of a time that is thereciprocal of the Doppler frequency. Specifically, if the maximumDoppler frequency stipulated in a radio communication system to whichtransmitting apparatus 100 and receiving apparatus 500 belong isdesignated fd, modulation method information signals MX and MY and errorcorrection method information signals CX and CY should be arranged atlocations separated by a time of approximately 1/fd.

By this means, even if the received field strength declines due tofading, the decline in the received field strength at one or other ofthe locations of modulation method information signals MX and MY anderror correction method information signals CX and CY can be kept withinpermissible values, enabling the error rate of modulation methodinformation and error correction method information to be kept down.

For example, if discrete locations are selected as extremely closelocations, when the received field strength declines due to fading thereceived field strength of all discretely arranged symbols will decline,and the error rate of all modulation method and error correction methodinformation will increase. Considering this point, the locations atwhich modulation method and error correction method information isarranged may be decided simply as near the start, near the middle, ornear the end, within a frame.

According to the above configuration, when the modulation method orerror correction method is switched adaptively according to the state ofthe propagation path, the transmitting side transmits with modulationmethod information symbols MX and MY and error correction methodinformation symbols CX and CY arranged discretely within a transmitframe, and the receiving side detects the reception power of discretelyarranged modulation method information symbols MX and MY and errorcorrection method information symbols CX and CY at each location, findsthe final modulation method and error correction method by weighting thediscretely arranged modulation method information and error correctionmethod information according to the size of the reception power, andobtains a demodulated and decoded signal based thereon, thereby makingit possible to obtain a transmitting apparatus 100 and receivingapparatus 500 that enable degradation of communication quality to besuppressed even in the event of noise or propagation path fluctuations.

Also, by making modulation method information symbols MX and MY anderror correction method information symbols CX and CY not a singlesymbol but a plurality of symbols (in the case of this embodiment, threesymbols), it is possible for modulation method information and errorcorrection method information to be transmitted more accurately.

Furthermore, by transmitting modulation method information symbols MXand MY and error correction method information symbols CX and CYmodulated using BPSK modulation or QPSK modulation, which are modulationmethods tolerant of fading and propagation path fluctuations, it ispossible for modulation method information and error correction methodinformation to be transmitted more accurately.

In this embodiment, a case has been described in which final modulationmethod information and error correction method information is obtainedby weighting discretely arranged modulation method information and errorcorrection method information according to reception power, but thepresent invention is not limited to this, and it is also possible foronly the modulation method information and error correction methodinformation with the larger reception power to be taken as the finalmodulation method information and error correction method information.For example, when, as shown in FIG. 8, the reception power of modulationmethod information MY and error correction method information CY ishigher than the reception power of modulation method information MX anderror correction method information CX, modulation method information MYand error correction method information CY may be selected.

Also, in this embodiment, a case has been described in which thetransmission power of symbols indicating the modulation method and errorcorrection method is made the same as the transmission power of datasymbols and pilot symbols, but if the transmission power (that is, themaximum signal amplitude) of symbols indicating the modulation methodand error correction method is made higher than the transmission power(maximum signal amplitude) of other symbols, it is possible formodulation method information and error correction method information tobe received with greater accuracy by the receiving side.

Moreover, in this embodiment, a case has been described in which atransmit frame such as that shown in FIG. 3 is configured bytransmitting apparatus 100, but the frame configuration is not limitedto that shown in FIG. 3. Similarly, modulation method informationsymbols and error correction method information symbols are inserted asthree consecutive symbols at two discrete locations, but this is not alimitation.

Furthermore, the configurations of a transmitting apparatus, receivingapparatus, and modulation method and error correction method estimationsection according to the present invention are not limited to thoseshown in FIG. 2, FIG. 6, or FIG. 7. In particular, in this embodimentthe number of locations at which modulation method information and errorcorrection method information is discretely arranged is two, andtherefore in the configuration of modulation method and error correctionmethod estimation section 507 in FIG. 7 two modulation method and errorcorrection method information determination sections and two modulationmethod and error correction method information reception powercalculation sections are provided, but these numbers are in accordancewith the number of discretely inserted modulation method informationsymbols and error correction method information symbols, and a numbermay be provided accordingly.

In addition, in this embodiment, a case has been described in whichmodulation method information and error correction method informationare transmitted, but the same kind of effect as in this embodiment canalso be obtained when the present invention is applied to a transmittingapparatus and receiving apparatus between which only one of these istransmitted. For example, if the present invention is used in a systemin which only modulation method information is transmitted, it will bepossible for modulation method information to be transmitted correctlyto the receiving side.

Embodiment 2

FIG. 9, in which parts corresponding to those in FIG. 2 are assigned thesame codes as in FIG. 2, shows the configuration of a transmittingapparatus according to Embodiment 2 of the present invention.Transmitting apparatus 800 transmits a transmit signal arranged in amutually orthogonal plurality of subcarriers by means of OFDM(Orthogonal Frequency Division Multiplexing).

Specifically, by executing serial/parallel conversion processing on theoutput of frame configuration section 111 by means of a serial/parallelconversion section (S/P conversion section) 801, and then executinginverse Fourier transform processing on the parallel signals resultingfrom this processing by means of an inverse Fourier transform section(idft) 802, a transmit signal with the signal arrangement shown in FIG.10(A) or FIG. 10(B) is formed. Divisions in the frequency direction inFIG. 10(A) and FIG. 10(B) indicate subcarrier demarcations. That is tosay, FIG. 10(A) and FIG. 10(B) show examples in which a demodulatedsignal is transmitted using 10 mutually orthogonal subcarriers.

In the example shown in FIG. 10(A), an error correction methodinformation symbol is arranged discretely in subcarriers of differentfrequency at the same time, and a modulation method information symbolis arranged discretely in subcarriers of different frequency at the sametime. By using this kind of arrangement, even if frequency selectivefading that causes a decline in the gain of a certain frequency occurson the propagation path, for example, the signal level of one errorcorrection method information symbol and modulation method informationsymbol is maintained, enabling an error correction method informationsignal and modulation method information signal with a signal levelgreater than or equal to a predetermined value to be obtained on thereceiving side.

In the example shown in FIG. 10(B), an error correction methodinformation symbol is arranged at different times in a subcarrier of thesame frequency, and a modulation method information symbol is arrangedat different times in a subcarrier of the same frequency. By using thiskind of arrangement, even if propagation path fluctuations occur overtime, for example, the signal level of an error correction methodinformation symbol and modulation method information symbol at aparticular point in time is maintained, enabling an error correctionmethod information signal and modulation method information signal witha signal level greater than or equal to a predetermined value to beobtained on the receiving side.

The configuration of a receiving apparatus that receives an OFDM signaltransmitted by transmitting apparatus 800 is shown in FIG. 11. In FIG.11, in which parts corresponding to those in FIG. 6 are assigned thesame codes as in FIG. 6, receiving apparatus 1000 executes Fouriertransform processing on the output of radio section 502 by means of aFourier transform section (dft) 1001, and executes parallel/serialconversion of the signal resulting from Fourier transform processing bymeans of a parallel/serial conversion section (P/S conversion section)1002. As a result, a signal with the frame configuration shown in FIG. 3is obtained from the orthogonal frequency division multiplexed receivedsignal. Subsequent processing is the same as that described inEmbodiment 1.

According to the above configuration, when an OFDM signal is formed froma transmit signal containing an error correction method informationsignal and modulation method information signal, and transmitted, byarranging the error correction method information signal and modulationmethod information signal discretely in different subcarriers or attemporally separated locations in the same subcarrier, it is possiblefor an error correction method information signal and modulation methodinformation signal of the necessary signal level or higher to beobtained on the receiving side. As a result, the modulation method anderror correction method of a digitally modulated signal can bedetermined correctly on the receiving side.

In this embodiment a case has been described in which OFDM modulationprocessing is executed on output of frame configuration section 111—thatis, OFDM modulation processing is executed on a signal with the frameconfiguration shown in FIG. 3—but the present invention is not limitedto this, and the key point is that, when an OFDM signal is formed from atransmit signal containing an error correction method information signaland modulation method information signal, and transmitted, the same kindof effect as in the above-described embodiment can be obtained if theerror correction method information signal and modulation methodinformation signal are discretely arranged in different subcarriers orat temporally separated locations in the same subcarrier.

The present invention is not limited to the above-described embodiments,and various variations and modifications may be possible withoutdeparting from the scope of the present invention.

A transmitting apparatus according to the present invention has aconfiguration comprising a modulation method information signalgeneration section that generates an information signal relating to themodulation method of information symbols, an error correction methodinformation signal generation section that generates an informationsignal relating to the error correction method of information symbols, aframe forming section that forms a transmit frame by discretelyarranging a modulation method information signal and/or error correctionmethod information signal, and a transmission section that transmits thetransmit frame.

According to this configuration, since a modulation method informationsignal and/or error correction method information signal are/is arrangeddiscretely, the possibility is low that both discretely arranged signalswill degrade even if the transmit signal experiences fading orpropagation path fluctuations. As a result, it is possible for themodulation method information signal and/or error correction methodinformation signal to be restored accurately on the receiving side.

A transmitting apparatus according to the present invention has aconfiguration wherein a modulation method information signal generationsection and/or error correction method information signal generationsection generate(s) a modulation method information signal or errorcorrection method information signal comprising a plurality of symbols.

According to this configuration, propagation path error tolerance isimproved compared with the case where a modulation method informationsignal and/or error correction method information signal are/is formedby a single symbol, making it possible for the modulation methodinformation signal and/or error correction method information signal tobe restored more accurately on the receiving side.

A transmitting apparatus according to the present invention has aconfiguration wherein a frame forming section discretely arranges amodulation method information signal and/or error correction methodinformation signal at locations separated by a predetermined time ormore according to the Doppler frequency.

According to this configuration, even if the received field strengthdeclines due to fading, the decline in the received field strength atone or other of the locations of discretely arranged modulation methodinformation signals and error correction method information signals canbe kept within permissible values, enabling the error rate of modulationmethod information and error correction method information to be keptdown even when fading occurs. For example, if discrete locations areselected as extremely close locations, when the received field strengthdeclines due to fading the received field strength of all discretelyarranged symbols will decline, and the error rate of all modulationmethod and error correction method information will increase. In thisconfiguration this point is taken into consideration, and discretelyarranged locations are selected optimally taking account of the Dopplerfrequency, which is closely linked to fading.

A transmitting apparatus according to the present invention has aconfiguration wherein a transmission section transmits a transmit framewith the maximum signal point amplitude of a modulation methodinformation signal and/or error correction method information signalmade larger than the maximum signal point amplitude of an informationsymbol.

According to this configuration, since the signal point interval of amodulation method information signal and error correction methodinformation signal is increased, it is possible for the modulationmethod information signal and/or error correction method informationsignal to be restored more accurately on the receiving side.

A transmitting apparatus according to the present invention has aconfiguration whereby a modulation method information signal and/orerror correction method information signal are/is transmitted modulatedby means of BPSK modulation or QPSK modulation.

According to this configuration, since highly error tolerant BPSKmodulation or QPSK modulation is used as the information signal and/orerror correction method information signal modulation method, it ispossible for the modulation method information signal and/or errorcorrection method information signal to be restored more accurately onthe receiving side.

A transmitting apparatus according to the present invention has aconfiguration whereby a modulation method information signal and/orerror correction method information signal are/is arranged discretely ina mutually orthogonal plurality of subcarriers.

According to this configuration, even when frequency selective fadingoccurs, the possibility is high that the decline in signal level due tofading will be small for the modulation method information signal and/orerror correction method information signal of at least one subcarrieramong the modulation method information signals and/or error correctionmethod information signals arranged discretely in different subcarriers,and it is therefore possible for an error correction method informationsignal and/or modulation method information signal of the necessarysignal level or higher to be obtained on the receiving side.

A receiving apparatus according to the present invention receives anddemodulates a received signal that contains an information signal, amodulation method information signal relating to the modulation methodof the information signal, and an error correction method informationsignal relating to the error correction method of the informationsignal, and wherein the modulation method information signal and errorcorrection method information signal are arranged at discrete locationswithin the same frame; and this receiving apparatus comprises areception power detection section that detects reception power for thediscretely arranged modulation method information signal and errorcorrection method information signal at the respective locations, adecision section that decides the modulation method and error correctionmethod by performing weighting according to the respective receptionpower on a modulation method information signal and error correctionmethod information signal arranged at a location corresponding toreception power detected by the reception power detection section, and asignal selection section that selects a demodulated signal obtained byexecuting demodulation processing and error correction processingcorresponding to the modulation method and error correction methoddecided by the decision section.

According to this configuration, attention is paid to the fact thaterrors are fewer in demodulation the higher the reception power at thelocation of a signal, and the modulation method and error correctionmethod are decided by weighting a discretely arranged modulation methodinformation signal and error correction method information signal withreception power. As a result, the correct modulation method and errorcorrection method can be decided, and by performing demodulationprocessing and error correction processing in accordance therewith, ahigh-quality received signal can be obtained.

A receiving apparatus according to the present invention receives anddemodulates a received signal that contains an information signal, amodulation method information signal relating to the modulation methodof the information signal, and an error correction method informationsignal relating to the error correction method of the informationsignal, and wherein the modulation method information signal and errorcorrection method information signal are arranged at discrete locationswithin the same frame; and this receiving apparatus comprises areception power detection section that detects reception power for thediscretely arranged modulation method information signal and errorcorrection method information signal at the respective locations, adecision section that decides the modulation method and error correctionmethod by selecting a modulation method information signal and errorcorrection method information signal arranged at a locationcorresponding to reception power detected by the reception powerdetection section, and a signal selection section that selects ademodulated signal obtained by executing demodulation processing anderror correction processing corresponding to the modulation method anderror correction method decided by the decision section.

According to this configuration, attention is paid to the fact thaterrors are fewer in demodulation the higher the reception power at thelocation of a signal, and of the discretely arranged modulation methodinformation signals and error correction method information signals, themodulation method and error correction method of the signals with higherreception power are selected. As a result, accurate modulation methodand error correction method signals with few errors in demodulation canbe obtained, and by performing demodulation processing and errorcorrection processing in accordance therewith, a high-quality receivedsignal can be obtained.

A transmission method according to the present invention generates amodulation method information signal relating to the modulation methodof information symbols and also generates an error correction methodinformation signal relating to the error correction method ofinformation symbols, forms a transmit frame by discretely arranging amodulation method information signal and/or error correction methodinformation signal, and transmits the transmit frame.

According to this method, since a modulation method information signaland/or error correction method information signal are/is arrangeddiscretely, the possibility is low that both discretely arranged signalswill degrade even if the transmit signal experiences fading orpropagation path fluctuations. As a result, it is possible for themodulation method information signal and/or error correction methodinformation signal to be restored accurately on the receiving side.

A reception method according to the present invention receives anddemodulates a received signal that contains an information signal, amodulation method information signal relating to the modulation methodof the information signal, and an error correction method informationsignal relating to the error correction method of the informationsignal, and wherein the modulation method information signal and errorcorrection method information signal are arranged at discrete locationswithin the same frame; and this reception method detects reception powerfor the discretely arranged modulation method information signal anderror correction method information signal at the respective locations,decides the modulation method and error correction method by selecting amodulation method information signal and error correction methodinformation signal arranged at a location corresponding to detectedreception power, and selects a demodulated signal obtained by executingdemodulation processing and error correction processing corresponding tothe decided modulation method and error correction method.

According to this method, attention is paid to the fact that errors arefewer in demodulation the higher the reception power at the location ofa signal, and of the discretely arranged modulation method informationsignals and error correction method information signals, the modulationmethod and error correction method of the signals with higher receptionpower are selected. As a result, accurate modulation method and errorcorrection method signals with few errors in demodulation can beobtained, and by performing demodulation processing and error correctionprocessing in accordance therewith, a high-quality received signal canbe obtained.

As described above, according to the present invention, in acommunication system in which propagation path error tolerance isimproved by switching the modulation method or error correction methodadaptively according to the state of the propagation path, bytransmitting signals indicating the modulation method and errorcorrection method used by the transmitting side arranged at discretelocations within the same frame, it is possible for the modulationmethod and error correction method of a digitally modulated signal to bedetermined correctly on the receiving side, enabling communicationquality to be improved.

This application is based on Japanese Patent Application No. 2001-356400filed on Nov. 21, 2001, entire contents of which are expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is applicable, for example, to a digital radiocommunication system in which the modulation method or error correctionmethod is changed adaptively according to the propagation pathenvironment or the like.

What is claimed:
 1. A transmission frame generating device forgenerating a transmission frame, comprising: a control informationsignal generator that generates a modulation method information signalindicating a modulation method of a data signal and an error correctionmethod information signal indicating an error correction method of thedata signal; and a frame former that forms the transmission frame byrepeating and discretely arranging the same modulation methodinformation signal on a first multiple of a plurality of subcarriers ona frequency axis and by repeating and discretely arranging the sameerror correction method information signal on a second multiple of theplurality of the subcarriers on the frequency axis.
 2. The transmissionframe generating device according to claim 1, wherein the frame formerforms the transmission frame by repeating and discretely arranging thesame modulation method information signal on the first multiple of theplurality of subcarriers at the same first time and the same errorcorrection method information signal on the second multiple of theplurality of the subcarriers at the same second time.
 3. Thetransmission frame generating device according to claim 1, wherein theframe former forms the transmission frame in which the same modulationmethod information signal is located prior to the same error correctionmethod information signal.
 4. The transmission frame generating deviceaccording to claim 2, wherein the frame former forms the transmissionframe in which the same modulation method information signal is locatedprior to the same error correction method information signal.
 5. Thetransmission frame generating device according to claim 1, furthercomprising: a modulator that modulates the data signal, the modulationmethod information signal and the error correction method informationsignal, wherein the modulation method information signal and the errorcorrection method information signal are modulated using QPSK or BPSKmodulation.
 6. The transmission frame generating device according toclaim 2, further comprising: a modulator that modulates the data signal,the modulation method information signal and the error correction methodinformation signal, wherein the modulation method information signal andthe error correction method information signal are modulated using QPSKor BPSK modulation.
 7. The transmission frame generating deviceaccording to claim 1, wherein each transmission frame includes a firstperiod and a second period; wherein the first period includes themodulation method information signal and the error correction methodinformation signal; and wherein the second period includes the datasignal.
 8. The transmission frame generating device according to claim2, wherein each transmission frame includes a first period and a secondperiod; wherein the first period includes the modulation methodinformation signal and the error correction method information signal;and wherein the second period includes the data signal.
 9. Thetransmission frame generating device according to claim 1, wherein alocation of the first multiple of the plurality of subcarriers on thefrequency axis is the same as a location of the second multiple of theplurality of subcarriers on the frequency axis.
 10. The transmissionframe generating device according to claim 1, wherein the samemodulation method information signals are arranged into two discretemodulation groups, the same modulation method information signals beingadjacent to each other in each of the modulation groups, and, whereinthe same error correction method information signals are arranged intotwo discrete error correction groups, the same error correction methodinformation signals being adjacent to each other in each of the errorcorrection groups.
 11. The transmission frame generating deviceaccording to claim 1, wherein the data signal, the modulation methodinformation signal and the error correction method information signalare transmitted by using the transmission frame.
 12. The transmissionframe generating device according to claim 1, wherein the modulationmethod information signal indicates a selected modulation method from aplurality of modulation methods of the data signal and the errorcorrection method information signal indicates a selected errorcorrection method from a plurality of error correction methods of thedata signal.
 13. A transmission frame generating method for generating atransmission frame, comprising: generating a modulation methodinformation signal indicating a modulation method of a data signal andan error correction method information signal indicating an errorcorrection method of the data signal; and forming the transmission frameby repeating and discretely arranging the same modulation methodinformation signal on a first multiple of a plurality of subcarriers ona frequency axis and by repeating and discretely arranging the sameerror correction method information signal on a second multiple of theplurality of subcarriers on the frequency axis.
 14. The transmissionframe generating method according to claim 13, wherein the forming oftransmission frame is performed by repeating and discretely arrangingthe same modulation method information signal on the first multiple ofthe plurality of subcarriers at the same first time and the same errorcorrection method information signal on the second multiple of theplurality of the subcarriers at the same second time.
 15. Thetransmission frame generating method according to claim 14, furthercomprising: transmitting the modulation method information, the errorcorrection method information and the data signal by using thetransmission frame.
 16. The transmission frame generating methodaccording to claim 15, wherein the forming of transmission frame isperformed by forming the transmission frame in which the same modulationmethod information signal is located prior to the same error correctionmethod information signal.
 17. The transmission frame generating methodaccording to claim 13, wherein the modulation method information signaland the error correction method information signal are modulated usingQPSK or BPSK modulation.
 18. The transmission frame generating methodaccording to claim 13, wherein each transmission frame includes a firstperiod and a second period; wherein the first period includes themodulation method information signal and the error correction methodinformation signal; and wherein the second period includes the datasignal.
 19. The transmission frame generating method according to claim13, wherein a location of the first multiple of the plurality ofsubcarriers on the frequency axis is the same as a location of thesecond multiple of the plurality of subcarriers on the frequency axis.20. The transmission frame generating method according to claim 13,wherein the same modulation method information signals are arranged intotwo discrete modulation groups, the same modulation method informationsignals being adjacent to each other in each of the modulation groups,and, wherein the same error correction method information signals arearranged into two discrete error correction groups, the same errorcorrection method information signals being adjacent to each other ineach of the error correction groups.
 21. The transmission framegenerating method according to claim 13, wherein the modulation methodinformation signal indicates a selected modulation method from aplurality of modulation methods of the data signal and the errorcorrection method information signal indicates a selected errorcorrection method from a plurality of error correction methods of thedata signal.